<!DOCTYPE html>
<html>
<body>
<select id="target1" size="1">
    <option value="One">One</option>
    <option value="Two">Two</option>
    <option value="Three">Three</option>
    <option value="Four">Four</option>
</select>
<select id="target2" size="2">
    <option value="Um">Um</option>
    <option value="Dois">Dois</option>
    <option value="Tres">Tres</option>
    <option value="Quatro">Quatro</option>
</select>
<script>
    window.inputEventCounter = 0;

    function increaseInputEventCounter () {
        window.inputEventCounter++;
    }

    document.querySelector('#target1').addEventListener('input', increaseInputEventCounter);
    document.querySelector('#target2').addEventListener('input', increaseInputEventCounter);
</script>
</body>
</html>